The air-sparged hydrocyclone (ASH) has been recognized as one of the basic designs for flotation equipment in the seventh edition of Perry's Chemical Engineers' Handbook and is shown in FIG. 1A. Although the ASH is included in a paragraph on Flotation Columns, it functions differently from the traditional flotation column. The ASH technology was originally developed at the University of Utah for fast flotation of fine particles from a mineral suspension. The original ASH unit consists of two concentric right-vertical tubes (a porous inner tube 2 and an outer cylinder jacket 4) and a conventional cyclone header 6 at the top. The porous inner tube is constructed of plastic, ceramic, or stainless steel and allows for the sparging of air, or other fluid. The outer nonporous tube provides an air jacket to secure even distribution of the gas phase through the porous tube.
The aqueous phase is fed tangentially at the top through an upper inlet 8 the cyclone header 6 to develop a swirl flow adjacent to the internal surface of the porous tube, leaving an air core 10 centered on the axis of the ASH unit, as shown in FIG. 1A. A gas is injected via inlets 12 into the cylinder jacket 4 and sparging through the porous inner tube 2. The high-velocity swirl flow shears the sparged gas to produce a high concentration of small bubbles 14 as shown in the cross-section of FIG. 1B. Hydrophobic particles in the slurry, after attachment to the bubbles, are significantly reduced in their tangential velocity and transported radially into a froth phase 10, which forms along the cylindrical axis. Hydrophilic particles generally remain in the slurry phase and are discharged as an underflow product 15 through the annular opening created by the froth pedestal 16. A vortex finder 18 can be used to direct the air-froth core to an overflow outlet 19.
While the ASH has shown great promise for use in a variety of fields, the materials used, and the necessary specifications of portions of the design, in particular the porous inner tube, can be expensive. Furthermore, the ASH design is limited to sparging, or other contact requiring a gas traveling through the porous inner tube. Such a design additionally generally requires a significant and often unwanted pressure drop within the ASH.